A common means of preparing liquid specimens for microscopic examination has been to place a small quantity of the fluid on a flat, transparent slide plate and then placing a thin flat transparent cover slip over the specimen. The cover slip presses against the plate and spreads the fluid into a thin film in the space between the two elements. Thereafter, the liquid is retained in the space between the two elements by capillary action, that is, by the attraction of the liquid molecules for each other and for those of the solid materials forming the slide and cover slip. It is the space formed between the two elements in which sample specimens are retained that is hereinafter referred to as the capillary chamber. The thus prepared slide with the specimen is then placed on a microscope stage and is microscopically examined through the transparent cover slip.
One purpose for which a specimen so prepared is examined is to permit quantitative microscopic analysis of particulate matter in the fluid. Fluids which are typically examined by such procedures include urine, blood, spinal fluid, sputum and cell cultures. When the specimen has been spread to a film of generally uniform thickness, the technician is able to count the number of solid particulars, cells and the like in a given area of the specimen and this count is indicative of the content of the specimen per unit volume thereof. The actual volume of fluid confined beneath a given area of the cover slip is dependent upon several variables, among them being the size of the drop of liquid applied to the slide plate, the viscosity of the fluid, the force applied in squeezing the cover slip against the plate and the flatness of the two elements in their confronting relationship. The distribution of solid particles in the specimen, particularly larger particles, can be affected by the squeezing action, and slippage can occur between the cover slip and the plate, thereby possibly adversely affecting the accuracy of the examination. Because the thickness of sample depends on the amount of sample placed on the slide, as much as a 50-200% error can be introduced.
Wet mount slides of the type mentioned above have commonly been made of glass and normally a single specimen can be examined by one combination of plate and cover slip. Also, a relatively significant amount of dexterity, manipulation and skill is necessary to apply the specimen on the plate, place the cover slip thereon and handle the prepared slide until examination is completed. If an excess amount of the specimen is placed on the plate, it may be forced out of the space between the plate and the cover slip when they are positioned together. Removing the excess specimen without physically disturbing the position of two elements requires some skill. Furthermore, the entrapment of air between the plate and the cover slip can form undesirable bubbles which interfere with the accuracy of the examination. Another limitation of conventional wet mount slides has been the general impracticality of applying more than one specimen per slide. The contamination due to the intermixing of specimens is unavoidable where the spreading of the samples beneath the cover slip is uncontrolled. The cover slip also serves to protect the specimen from contamination by the technician, the objective of the microscope, and the environment.
The results of any analysis done by a technician are necessarily dependent on the skill and experience of that technician. For consistency, uniformity, and reproducability of results, it is important that sample sizes for a particular fluid be controlled both by the amount of specimen analyzed, and the depth of the capillary chamber for optimum accuracy.
Efforts have been made to provide unitary liquid specimen holders which overcome the disadvantages of the two-part slide mentioned above. Two of such examples of prior art are the U.S. Pat. No. issued to White, 3,961,346 and Elkins, U.S. Pat. No. 3,777,283 (referred to as the '346 White patent and the '283 Elkins patent, respectively). Both attempts have been less than completely satisfactory in dealing with the problems previously discussed. In the device of the '346 White patent, the two surfaces forming the capillary chamber are not parallel thereby resulting in a variation in the density of the particulate matter, depending upon the lateral position within the chamber. To deal with the problem of air bubble entrapment in the capillary chambers, the devices of the '346 White patent and '283 Elkins patent both make use of smoothly curved side walls to prevent any sharp corners where bubbles might collect. However, because both systems are closed systems, when the specimen is introduced into the chamber, undesirable air bubbles are often formed which are difficult to remove.
The devices in both the '346 White patent and '283 Elkins patent are one piece molded plastic devices with no possibility of adjustment of the thickness of the capillary chamber, that is, the spacing between the plate and cover slip. The capillary chambers of such slides can conveniently be molded with a spacing of 0.005 inch (0.127 mm) to about 0.015 inch (0.381 mm), and it has not been practical to directly mold a slide having smaller spacing, even though a thinner specimen chamber could at times be desirable.
The removal of excess sample remains a problem with both the inventions of the '346 White patent and '283 Elkins patent since both require manual manipulation and/or towelling off of the excess by the technician.
The U.S. Pat. No. 2,039,219 to Hausser discloses a wet mount examination slide wherein the slide plate, formed in a base member, is surrounded by overflow channels. The Hausser cover slip, however, has no positive interconnection means to the base member and, consequently, the relative and exact positioning of cover slip to plate surface is difficult to maintain while charging the examination chamber.
The present invention allows excess sample to flow freely out of the capillary chamber and into a trough on the slide while avoiding the problems inherent in Hausser.